This invention relates to semiconductor devices, and more particularly to clock generator circuits of the type used in VLSI semiconductor memory devices.
Semiconductor integrated circuit devices are being constructed with ever-increasing circuit density, Dynamic MOS memory devices are now being developed containing 256K bits, and 1-Megabit devices will soon be designed. These devices require scaling of the transistor sizes, i.e. reduction in the physical size of each part of the transistor, including the thickness of the gate oxide. With gate oxide of 200 .ANG. thickness and supply voltage of +5V, the electric field across the gate oxide can cause failures due to dielectric breakdown. In particular, booted nodes are needed in clock generator circuits or the like to assure full logic-level outputs, and transistors connected to such booted nodes are subjected to excess electric field across the gate oxide.
It is the principal object of this invention to provide improved clock generator circuits for semiconductor integrated circuits such as memory devices. Another object is to provide improved protection from overvoltage for the gate oxide of MOS field-effect transistors as may be used in circuits having high-level booted nodes.